Just lay out the system on paper first get the GPM's of each type of head then you'll know how many zones and how many heads per zone.
You also hafta lay out the coverage per head and overlap and ect. ect. ect.
Most times you need at least 50 PSI, but then again it's all subjective to the type and number of heads and zones.
We used to lay out those aggravatin' things when I was drilling wells.
